Imaging devices are of common use for scanning a marking on an item, as illustrated, for example, with the optical scanners disclosed in the U.S. Pat. Nos. 6,352,204 B2, 7,357,326 B2, 7,370,801 B2 and 7,419,098 B2, Such marking may be a barcode (linear or 2-D like a datamatrix) or any other pattern including identification data corresponding to the item. In some cases, a marking on a surface of an item is invisible or hardly visible to the unaided eye (a pattern printed in phosphorescent, luminescent or fluorescent inks, for example) and/or can be detected only under illumination with specific light, in the UV or IR regions of the spectrum for example. Moreover, even if the marking can be detected with visible light, its size may be small or it may include fine details of small scales so that said marking is difficult to read, which makes good illumination conditions necessary. Conventional light sources for scanners (depending on which part of the spectrum is to be used for detection of the marking) are incandescent lamps (typically for wavelengths between about 400 nm to about 2500 nm), flash lamps (like Xenon high-pressure flash lamp, for example), laser or Light-Emitting-Diodes (LEDs, emitting in the UV, visible or IR regions, typically for wavelengths from about 250 nm to about 1 micron). Conventional photodetectors for scanners are cameras of the CMOS or CCD type, photodiodes (single or arrays), phototransistor or photoresistance circuits, linear CMOS or CCD sensors.
A conventional optical scanner (which may be hand-held or fixed) comprises a light source (which may include filters) for illuminating a zone on an item with appropriate light, an illuminator (which may include focusing means) for delivering light received from said light source appropriately to said zone, means for collecting light reflected from said zone and transmitting it back to a photodetector, a processing unit for analyzing a signal delivered by the photodetector (and detecting/reading or decoding data associated with a marking within said zone), and a control unit for controlling the illumination source and the processing unit.
Conventional hand-held scanners (either corded or cordless) generally further include a power module for supplying the scanner with power and may also comprise a radio module for wireless communication (over Wi-Fi for example), a display module (a liquid crystal display LCD, or kinescope display, for example) for displaying measured data or scanning parameters, and a controlling interface for inputting scan conditions (including buttons having multiple functions and an ON/OFF switch button). Conventional optical scanners may further incorporate an RFID (Radio Frequency Identification) circuit for reading RFID chips on a scanned item (see, for example, U.S. Pat. No. 6,264,106 B1), thus allowing the scanner to read a combined optical/RFID marking.
A classical problem with an optical scanner is to illuminate a zone, at a level of an item's reflective surface comprising a marking, homogeneously and with sufficient light intensity, so that the detector of the scanner is capable to read said marking from the reflected light, while minimizing stray light and avoiding “hot spots” on the illuminated surface which degrade the contrast and may cause severe image processing problems; the detection of the marking may even fail if the image sensor saturates. Moreover, the above mentioned problem can, be enhanced in case of curved reflective surfaces.
The above cited prior art documents have considered this problem (see, for example, col. 1, lines 36-51 of U.S. Pat. No. 6,352,204 B2; col. 2, lines 16-19 of U.S. Pat. No. 7,357,326 B2; col. 2, lines 6-17 of U.S. Pat. No. 7,370,801 B2 and col. 2, lines 1-11 of U.S. Pat. No. 7,419,098 B2) and proposed some specific illumination techniques.
Document U.S. Pat. No. 6,352,204 B2 discloses illuminating a zone on an item at low incidence angle so as to minimize a “wash out effect” caused by shiny or irregular surfaces. However, there is a remaining problem with stray light.
Documents U.S. Pat. Nos. 7,357,326 B2, 7,370,802 B2 and 7,419,098 B2 disclose using a illuminator having a nosepiece, in the shape of a truncated pyramid, for directly illuminating a zone on an item by placing the converging end of said nosepiece near said zone so that light from the light source reaches only the intended zone while being shielded from much of the ambient light. The opposite diverging end of the nosepiece receives light from the light source. However, there are still some problems with direct reflection of light (back to the photodetector) on the internal face of the nosepiece (even if this face may be an irregularly uneven reflective one so as to scatter light) and also possible “light spots” on the reflective surface of the item.